In
a small bowl, stir together oil, yogurt, and sugar. Mix in eggs. Add
zucchini, water, and vanilla; stir. In a separate large bowl, sift
together flour, baking soda, salt, baking powder, and spices. Add the
wet ingredients to the dry and stir just until combined.

Pour
half the batter into the pan. Then add cocoa powder and chocolate to
the remaining half. Pour chocolate batter on top of plain batter.

Bake
until wooden pick inserted into center comes out clean, about 1 hour.
Cool 10 minutes, and remove from pan. Store in refrigerator.